She's corrupted by darkness.

Mai has been corrupted all of her life, first by her father and then by the stone of darkness that he passed down to her when she was 17. She has a rather concealed personality, usually leaving her face blank so that no one really knows what she's thinking. Emotions are a distraction. Showing your emotions is a weakness. She is however rather childish, outwardly sweet but sometimes its a bit too sickly. There is often malice behind her smile and if she ever feels the need to do something pleasant for someone her darker side takes over. She knows she could be a good person if she tried but kindness shows weakness beside she has never been a really headstrong person, often just following what her darkness tells her to do.
The darkness creates many weapons for her, most of the time she draws daggers and short swords.
Mai has been trained from the moment she could crawl, with her father putting weights on her wrists and ankles to strengthen her. She has always been strong and appeared toned but her appearance is that of delicacy. She grew up alone, with no other friends but her father and his idea of fun was reading through books on the theory of inner strength and combat. After a while this was what fun was to her too. Her father died when she was 17, the darkness finally driving him so crazy that he threw himself off of the roof of their three storey house and broke his neck. She had to slip the necklace off of him before the ambulance arrived and took him away, she was the only person at his funeral. Since then Mai has lived alone, travelling from place to place, searching for the one thing that her father always ranted about. The stones of magic that were stolen from their family a long time ago. Now the darkness pulses within her, stronger and more dangerous than ever as she draws closer, after two years of searching she can almost taste the power that the stones will bring to her, her father says that with all of them she could raise the dead. She could get him back.